Up to now, plastics panels having a sound-proofing property are in wide use, because of their light weight, as external wall materials, interior lining materials and roofing materials for buildings, as sound-proof walls for high ways and railways, and for other like uses. Such plastic panels are commonly used by incorporating into the inside thereof, to be imparted sound-proofing property, porous materials, such as formed plastics and glass wool, or finely partitioned hollow cells.
However, such plastic panels having porous, hollow cell structures are all poor in sound absorbing and insulating effect in the low- and medium-pitched sound range (100-200 Hz), and cannot give a satisfactory sound absorbing and insulating effect for a wide range of pitches of sound.
Further, since they have predominantly continuous pores, they are poor in resistance to a local load and unsatisfactory in mechanical strength.
An example of panels for sound-proofing in the low- and medium-pitched sound range is a sound-proof panel obtained by filling sand particles into the inner space of a sandwich type panel disclosed in JP-A-53-72313.
In this method, however, it is difficult to fill sand particles into the inner space of the panel closely without leaving gaps in order to attain a sufficient sound-proofing characteristic. Moreover, since sand is weighty, it is difficult to obtain panels of light weight.
JP-A-5-279569 discloses a vibration-proofing material comprising a silicone gel having a specific pressure transmission characteristic and hollow microspheres formed of an inorganic material, such as aluminosilicate, incorporated thereinto. However, the material aims at vibration proofing and damping in the range of 100 Hz or less, and nothing is taught of the sound absorption and insulation property of the material in the disclosure.
The object of the present invention is, overcoming the above-mentioned difficulties, to provide a light-weight plastic sheet material having an excellent sound absorbing and insulating effect even in the low- and medium-pitched sound range and a sound absorbing and insulating plastic panel using the sheet material for use in buildings and sound-proof walls.